Class S radio frequency power amplifiers (RFPAs) use single-bit sequences to synthesize radio frequency (RF) signals. As Class S technology moves the digital-to-analog boundary towards the power amplifier output stage, an increase in integration relative to analog RF signal processing techniques is made possible.
Class S power amplifiers typically refer to those amplifiers that filter an applied bitstream, which encodes a desired modulated RF signal, to deliver the bitstream in high-power analog form. Bitstream generators used in Class S-based RF transmitters upshift baseband information to a desired carrier frequency while shaping single-bit quantization noise power away from a carrier frequency, FCARRIER. In Class S power amplifiers associated with a 2.14 gigahertz (GHz) cellular band, for example, the output stage of the amplifier is switched at a rate in excess of eight (8) billion transitions per second.